Carbon fiber (also known as graphite fiber or carbon graphite) is a material comprising fibers, e.g. about 5-10 μm in diameter, and composed mostly of carbon atoms. The carbon atoms are bonded together in crystals that are more or less aligned parallel to the long axis of the fiber. The crystal alignment gives the fiber high strength-to-volume ratio, thus making it very strong for its size. Several thousand carbon fibers are twisted together to form a yarn, which may be used by itself or woven into a fabric.
The properties of carbon fibers, such as high flexibility, high tensile strength, low weight, high resistance, high temperature tolerance and low thermal expansion, make them very popular in aerospace, civil engineering, wind turbines, military, motorsports, sporting goods, and numerous other applications. They are often combined with other materials to form a composite. When combined with a plastic resin and wound or molded it forms carbon fiber reinforced plastic, which is a very high strength-to-weight, extremely rigid, although somewhat brittle material.
Carbon fiber is, however, relatively expensive when compared to other fibers, such as glass fibers or plastic fibers. Therefore, the potential to recycle and reuse carbon fiber is commercially valuable and important. At the same time, numerous physical conditions, such as age, mechanical damage, temperature, temperature variation, ultraviolet (UV) light exposure, humidity, humidity variation, and chemical exposure, can damage and weaken carbon fiber, rendering its recycling less desirable and its reuse less suitable. Accordingly, there remains a need for a simple labeling or tagging system for carbon fiber that enables the facile detection of potential damage and/or weakening, as well as the source and type of the fiber, in order to assess the suitability of such carbon fiber for recycling and reuse in a variation of applications.